Classification of combustible gases

For gas supply of cities and industrial enterprises, various combustible gases are used, differing in origin, chemical composition and physical properties.

By origin, combustible gases are divided into natural, or natural, and artificial, produced from solid and liquid fuel.

Natural gases are produced from wells of pure gas fields or oil fields along the way with oil. Gaza oil fields are called passing.

Gases of pure gas deposits are mainly consisting of methane with a small content of heavy hydrocarbons. They are characterized by consistency of composition and calorificities.

Coming gases along with methane contain a significant amount of heavy hydrocarbons (propane and butane). The composition and calorific value of these gases fluctuate widely.

Artificial gases are produced in special gas factories, they are obtained as a by-product when burning coal at metallurgical factories, as well as oil processing factories.

Gases produced from stone coal, we in our country for urban gas supply are used in very limited quantities, and their share decreases all the time. At the same time, the production and consumption of liquefied hydrocarbon gases obtained from passing oil gases on gas-substituted plants and oil refining plants in oil processing are growing. Liquid hydrocarbon gases used for urban gas supply consist mainly of propane and butane.

Composition of gases

The type of gas and its composition is largely predetermined by the area of \u200b\u200bgas, the scheme and diameters of the gas network, the structural solutions of gas-melting devices and individual nodes of gas pipelines.

Gas consumption depends on the calorific value, and hence the diameters of the gas pipelines and the conditions of burning gas. When using gas in industrial installations, the combustion temperature and the rate of flame propagation and the constancy of the composition of the gas fuel composition of the gases, as well as the physicochemical properties, are primarily dependent on the type and method of producing gases.

Combustible gases represent mechanical mixtures of various gases<как го­рючих, так и негорючих.

In the combustible part of gaseous fuels included: hydrogen (H 2) -GAZ without color, taste and odor, lower calorific value is 2579 kkal / nm 3 \\methane (CH 4) - gas without color, taste and odor, is the main fuel part of natural gases, lower calorific value 8555 kcal / nm 3;carbon monoxide (CO) - gas without color, taste and odor, it turns out of the incomplete combustion of any fuel, very poisonous, lower calorific value 3018 kcal / nm 3;heavy-hydrocarbons (With PN T)This name<и формулой обозначается целый ряд углеводородов (этан - С2Н 6 , пропан - С 3 Нв, бутан- С4Н 10 и др.), низшая теплотворная способность этих газов колеблется от 15226 до 34890 kcal / nm *.

In a non-combustible part of gaseous fuels, carbon dioxide (CO 2), oxygen (O 2) and nitrogen (N 2).

The non-combustible part of the gases is customary to be called ballast. Natural gases are characterized by high caloriness and complete absence of carbon monoxide. At the same time (a number of deposits, mainly gas-mounted, containing a very poisonous (and aggressive gas-hydrogen sulfide (H 2 S). Most of the artificial coal gases contain a significant amount of high-tech gas - carbon monoxide (CO). Availability of oxide in gas Carbon and other poisonous substances are very undesirable, as they complicate the production of operational work and increase the risk when using gas. In addition to the main components, the composition of the gases includes various impurities, the specific value of which in percentage is negligible. However, it is not necessary to consider the gas pipelines. Even millions of cubic gas meters, the total amount of impurities reaches a considerable amount. Many impurities fall out in gas pipelines, which ultimately leads to a decrease in their capacity, and sometimes to the complete cessation of gas passage. Therefore, the presence of impurities in the gas must be taken into account as when designing gas pipelines. . And during operation.

The number and composition of impurities depend on the method of production or gas production and the degree of cleaning. The most harmful impurities are dust, resin, naphthalene, moisture and sulfur compounds.

Dust appears in Gaza in the production process (production) or during gas transportation in pipelines. Resin is a product of thermal decomposition of fuel and accompanies many artificial gases. In the presence of dust in the gas, the resin contributes to the formation of resin-mud plugs and blockage of gas pipelines.

Naphthalene is usually contained in artificial coal gases. At low temperatures, naphthalene falls in pipes and, together with other solid and liquid impurities, reduces the passage cross-section of gas pipelines.

Moisture in the form of vapors is contained in almost all natural and artificial gases. In natural gases, it falls in the gas field as a result of gases with the surface of the water, and the artificial gases are saturated with water in the process of "production. The presence of moisture in gas in significant amounts is undesirable, as it lowers the calorific value of the gas. In addition, the heat capacity of the vaporization , moisture when burning gas takes a significant amount of heat together with combustion products into the atmosphere. A large content of moisture about Gaza is undesirable also because, condensing when cooled gas in the "burden of movement of it in pipes, it can create water jams in the gas pipeline (in the lowest Points) you want to delete. This requires the installation of special condensate collectors and pumping them.

Sulbly compounds, as already noted, are hydrogen sulfide, as well as serougerod, mercaptan, etc. These compounds are not only harmful to people's health, but also cause significant corrosion of pipes.

Ammonia and cyanide compounds, which are mainly contained in coal gases, should be noted from other harmful impurities. The presence of ammonia and cyanide compounds leads to increased corrosion of pipe metal.

The presence of carbon dioxide and nitrogen in combustible gases is also undesirable. These gases are not involved in the combustion process, being a ballast that reduces the calorific value, which leads to an increase in the diameter of gas pipelines and to a decrease in the economic efficiency of the use of gaseous fuel.

The composition of the gases used for urban gas supply must meet the requirements of GOST 6542-50 (Table 1).

Table 1

The average values \u200b\u200bof the composition of natural gases of the most famous fields of the country are presented in Table. 2.

From gas deposits (dry)

Western Ukraine. . .	81,2	7,5	4,5	3,7	2,5	- .	0,1	0,5	0,735
SHEBELINSKOY ...................................	92,9	4,5	0,8	0,6	0,6	____ .	0,1	0,5	0,603
Stavropol region. .	98,6	0,4	0,14	0,06		-	0,1	0,7	0,561
Krasnodar region. .	92,9		0,5	-	0,5	_	0,01	0,09	0,595
Saratovskoe ...............................	93,4	2,1	0,8	0,4	0,3	Traces	0,3	2,7	0,576
Gazli, Bukhara region	96,7		0,35	0,4"			0,1	0,45	0,575
From gas-field deposits (passing)
Romashkino .................................			18,5	6,2	4,7		0,1	11,5	1,07
				7,4	4,6	____	Traces		1,112	__ .
Tuymase ...............................			18,4	6,8	4,6	____	0,1	7,1	1,062	-
Awed .......		23,5		9,3	3,5	____	0,2	4,5	1,132	-
Oily .......... ............................				2,5		. ___ .		1,5	0,721	-
Syzran oil ...............................	31,9	23,9 -	5,9	2,7	0,8	1,7	1,6	31,5	0,932	-
Ishimbay .................................	42,4		20,5	7,2	3,1	2,8			1,040	_
Andijan. ...............................	66,5	16,6	9,4	3,1	3,1	0,03	0,2	4,17	0,801 ;

Gas calorific value

The amount of heat released in full combustion of the unit of the amount of fuel is called calorific value (q) or, as sometimes they say, calorificness, or calorieness, which is one of the main characteristics of the fuel.

Gas calorific value are usually referred to 1 m 3,taken under normal conditions.

In technical calculations under normal conditions, the state of the gas is understood at a temperature of 0 ° C, and, at a pressure of 760 mm RT. Art.The volume of gas under these conditions is indicated nm 3.(normal cubic meter).

For industrial gas measurements according to GOST 2923-45 for normal conditions, the temperature of 20 ° C and pressure 760 mm RT. Art.The volume of gas attributed to these conditions, unlike nm 3.we will call m. 3 (cubic meter).

Gas calorific value (Q))expressed in kcal / nm eor in kcal / m 3.

For liquefied gases, calorific value belongs to 1 kg.

The highest (Q c) and low (Q H) caloriness are distinguished. The highest calorific value takes into account the heat of the condensation of water vapor generated during fuel combustion. The lower calorific value does not take into account the heat contained in the water vapor of combustion products, since water lines are not condensed, but are carried out with combustion products.

The concepts of q v and q h belong only to those gases, during the combustion of which water vapors are distinguished (to carbon oxide, which does not give water vapor, these concepts are not related).

In condensation of water vapors, heat is highlighted, equal to 539 kcal / kg.In addition, when cooled condensate to 0 ° C (only 20 ° C), the heat is distinguished in the amount of 100 or 80 kcal / kg.

In total due to the condensation of water vapors, heat is highlighted over 600 kcal / kg,what constitutes the difference between the highest and lower thermal power capability. For most gases used in urban gas supply, this difference is 8-10%.

The values \u200b\u200bof the calorificities of some gases are shown in Table. 3.

For urban gas supply, gases are currently used, having, as a rule, the caloriness of at least 3500 kcal / nm 3.This is explained by the fact that in conditions of cities, gas is served by pipes at considerable distances. With low calf, it is required to feed a large amount. It inevitably leads to an increase in the diameters of gas ducts and, as a result, an increase in metal components and means for the construction of gas networks, A.V. Next: and to an increase in operating costs. An essential disadvantage of low-calorie gases is even what, in most cases, they contain a significant amount of carbon monoxide, which increases the risk when using gas, as well as during maintenance of networks and installations.

Gas calorific capacity less than 3500 kcal / nm 3most often used in industry, where it is not required to transport it over long distances and it is easier to organize burning. For urban gas supply, gas caller is desirable to have a constant. Oscillations, as we have already installed, not more than 10% are allowed. A greater change in the calorific value of the gas requires new adjustment, and sometimes shifts of a large number of unified burners of household appliances, which is associated with significant difficulties.

What is fuel?

This is one component or a mixture of substances that are capable of chemical transformations associated with heat release. Different fuels are characterized by quantitative content of oxidizing agent, which is used to release thermal energy.

In a broad sense, fuel is an energy source, that is, potential species of potential energy.

Classification

Currently, fuel types are divided by an aggregative state on liquid, solid, gaseous.

A stone and firewood, anthracite, is counted to a solid natural look. Briquettes, coke, thermaltration is a variety of artificial solid fuel.

Liquids include substances having a substance of organic origin. The main components are: oxygen, carbon, nitrogen, hydrogen, sulfur. Artificial liquid fuels will be a variety of resins, fuel oil.

It is a mixture of a variety of gases: ethylene, methane, propane, butane. In addition to them, in the composition of gaseous fuels there are carbon dioxide and ditch, hydrogen sulfide, nitrogen, water vapor, oxygen.

Fuel Indicators

Main combustion rate. The formula for determining the calorific value is considered in thermochemistry. Eliminate "conditional fuel", which implies the heat of combustion 1 kilogram of anthracite.

Domestic furnace fuel is intended for burning in heating devices of minor power, which are located in residential areas, heat generators used in agriculture for drying feed, canning.

The specific heat combustion of fuel is such a value that demonstrates the amount of heat that is formed with the full combustion of the fuel with a volume of 1 m 3 or weighing one kilogram.

To measure this value, J / kg, J / M 3, Caloi / m 3 are used. To determine the heat of combustion, the method of calorimetry is used.

With an increase in the specific heat of the combustion of fuel, the specific fuel consumption is reduced, and the efficiency of the efficiency remains a valid value.

The heat of combustion of substances is the amount of energy released during the oxidation of solid, liquid, gaseous substance.

It is determined by the chemical composition, as well as the aggregate state of the combustable substance.

Features of combustion products

The highest and lower heat of combustion is associated with the aggregate state of water in the substances obtained after the combustion of fuel.

The highest heat combustion is the amount of heat allocated in full combustion of the substance. This magnitude includes the heat of the condensation of water vapor.

The lower working heat of combustion is the value that corresponds to heat release during combustion without taking into account the heat of the condensation of water vapor.

Hidden heat condensation is considered the energy of the condensation of water vapor.

Mathematical interconnection

The highest and lower heat combustion is related to the following ratio:

Q b \u003d q h + k (w + 9h)

where W is the amount by weight (in%) of water in a combustible substance;

H-amount of hydrogen (% by weight) in a combustible substance;

k - coefficient constituting the value of 6 kcal / kg

Methods for calculating

The highest and lowest heat of combustion is determined by two main methods: settlement and experimental.

Calorimeters are used for experimental calculations. First burn fuel on it. Heat, which will be released completely completely absorbed by water. Having an idea of \u200b\u200bthe mass of water, it can be determined by changing its temperature, the magnitude of its heat of combustion.

This technique is considered simple and efficient, it assumes only the ownership of information on technical analysis data.

In the calculated method, the highest and lowest heat of combustion is calculated by the Mendeleev formula.

Q p H \u003d 339C P + 1030H P -109 (O P -S P) - 25 W P (KJ / kg)

It takes into account the content of carbon, oxygen, hydrogen, water vapor, sulfur in the working composition (in percent). The amount of heat during combustion is determined taking into account the conditional fuel.

The heat combustion of gas allows preliminary calculations, detect the effectiveness of the use of a certain type of fuel.

Features of origin

In order to understand how much heat is allocated during the combustion of a certain fuel, it is necessary to have an idea of \u200b\u200bits origin.

In nature there are different variants of solid fuels that differ in each other with the composition and properties.

His education is carried out in several stages. First, peat is formed, then brown and stone coal is obtained, then anthracite is formed. The main sources of solid fuel formation are leaves, wood, needles. Fixing, parts of plants when exposed to air, destroy the fungi, form peat. Its cluster turns into a brown mass, then the brown gas is obtained.

At high pressure and temperature, the brown gas passes into the stone coal, then the fuel accumulates in the form of anthracite.

In addition to the organic mass, there is an additional ballast in the fuel. The organic consider that part that was formed from organic substances: hydrogen, carbon, nitrogen, oxygen. In addition to these chemical elements, there is a ballast in its composition: moisture, ash.

The furnace technique involves the allocation of the working, dry, as well as the combustible mass of the fuel of the fuel. The working mass is called fuel in the initial form entering the consumer. Dry mass is a composition in which there is no water.

Structure

The most valuable components are carbon and hydrogen.

These elements are contained in any form of fuel. In the peat and wood, the percentage of carbon reaches 58 percent, in a stone and brown corner - 80%, and in anthracite it reaches 95 percent by weight. Depending on this indicator, the amount of heat released during the combustion of fuel is changing. Hydrogen is the second most important element of any fuel. Combining oxygen, it forms moisture, which significantly reduces the thermal value of any fuel.

Its percentage ranges from 3.8 in combustible slates to 11 in fuel oil. As ballast, oxygen comes into fuel.

It is not a heat generation chemical element, so negatively reflects on the magnitude of the heat of its combustion. The combustion of nitrogen contained in a free or bound form in combustion products is considered harmful impurities, so its number is clearly limited.

The sulfur is part of the fuel in the form of sulfates, sulphides, as well as in the quality of sulfur gases. In hydration, sulfur oxides form sulfuric acid, which destroys boiler equipment, adversely affects vegetation and living organisms.

That is why sulfur is the chemical element, the presence of which in natural fuel is extremely undesirable. If you get inside the workstation, sulfur compounds cause substantial poisoning of the service personnel.

There are three types of ash depending on its origin:

• primary;
• secondary;
• tertiary.

The primary form is formed from minerals that are contained in plants. The secondary ash is formed as the result of entering plant residues and earth.

Tertiary ash is in the composition of fuel in the process of mining, storage, as well as its transportation. With substantial deposition of ash, heat transfer occurs on the surface of the heating of the boiler unit, reduces the heat transfer value to water from gases. A huge amount of ash is negatively reflected on the process of operation of the boiler.

Finally

The volatile substances have a significant impact on the combustion process of any type of fuel. The more their output, the volume will be the volume of the flame front. For example, stone coal, peat, easily light up, the process is accompanied by minor heat loss. Coke, which remains after removing volatile impurities, only mineral and carbon compounds have in its composition. Depending on the features of the fuel, the amount of heat change significantly.

Depending on the chemical composition, three stages of solid fuel formation are isolated: peat, browning, coal.

Natural wood is used in small boiler installations. Mainly use chip, sawdust, hill, bark, the firewood themselves is used in minor quantities. Depending on the wood breed, the magnitude of the heat released significantly changes.

As the heat of combustion decreases, the firewood acquire certain advantages: fast flammability, minimal ash, lack of sulfur traces.

Significant information on the composition of natural or synthetic fuel, its calorific value is an excellent way to carry out thermochemical calculations.

Currently, the real possibility of identifying the main variants of solid, gaseous, liquid fuel, which will become the most efficient and inexpensive to use in a particular situation.

Physico-chemical properties of natural gases

Natural gases have no color, smell, taste.

The main indicators of natural gases include: composition, heat of combustion, density, combustion temperature and ignition, explosability boundaries and explosion pressure.

Natural gases of pure gas deposits are mainly consisting of methane (82-98%) and other hydrocarbons.

In combustion gas, there are combustible and non-combustible substances. Fuel gases include: hydrocarbons, hydrogen, hydrogen sulfide. Non-flammable: carbon dioxide, oxygen, nitrogen and water vapor. The composition of their low and is 0.1-0.3% C0 2 and 1-14% N 2. After mining from gas, a toxic gas hydrogen sulfide is removed, the content of which should not exceed 0.02 g / m3.

The heat of combustion is the amount of heat allocated at full combustion of 1 m3 of gas. The heat of combustion in Kcal / m3, KJ / M3 gas is measured. The heat of the combustion of dry natural gas is 8000-8500 kcal / m 3.

The value calculated by the ratio of the mass to its own volume is called the density of the substance. The density is measured in kg / m3. The density of natural gas is completely dependent on its composition and is in the limits of C \u003d 0.73-0.85 kg / m3.

The most important feature of any combustible gas is heat-produceness, i.e. the maximum temperature is achieved with full combustion of gas, if the required amount of combustion air for combustion accurately corresponds to the chemical combustion formulas, and the initial gas temperature and air is zero.

The heat production capacity of natural gases is about 2,000 -2100 ° C, methane - 2043 ° C. The actual combustion temperature in the furnace is significantly lower than heat efficiency and depends on the combustion conditions.

The inflammation temperature is the temperature of the fuel-air mixture, the mixture at which lights up without a source of ignition. For natural gas, it is within 645-700 ° C.

All combustible gases are explosive, are able to ignite with light or spark. Distinguish bottom and upper concentration limit of flame distribution . The lower and upper concentration at which the mixture is possible. The lower limit of the explosive of gases is 3 ÷ 6%, the upper 12 ÷ 16%.

Borders of explosions.

A gas-air mixture having a gas amount of gas:

up to 5% - not lit;

from 5 to 15% - explodes;

more than 15% is lit when air is supplied.

The pressure during the explosion of natural gas is 0.8-1.0 MPa.

All combustible gases can cause human body poisoning. The main poisoning substances are: carbon monoxide (CO), hydrogen sulfide (H 2 S), ammonia (NH 3).

Natural gas there is no smell. In order to determine the leakage of gas odorizing (i.e., give it a specific smell). Conducting odorization is carried out by using ethyl mercaptan. They carry out odorization at gas distribution stations (GDS). If in the air, 1% of natural gas begins to feel his smell. Practice shows that the average rate of ethyl mercaptan for odorization of natural gas, which enters the city networks, should be 16 g per 1,000 m3 of gas.

Compared to solid and liquid fuels, natural gas wins in many ways:

Relative low cost, which is explained by an easier way of mining and transport;

The absence of ash and removal of solid particles into the atmosphere;

High heat combustion;

No preparation of fuel is required to burn;

The labor of those serving workers and the improvement of the sanitary and hygienic conditions of its work is facilitated;

Fighter conditions for automation of workflows.

Due to possible leaks through looseness in the compounds of the gas pipeline and in places of reinforcement, the use of natural gas requires special care and caution. Penetration into the room more than 20% of the gas can lead to suffocation, and if it has it, in a closed volume from 5 to 15%, can cause an explosion of a gas-air mixture. In case of incomplete combustion, toxic carbon monoxide is formed, which even at low concentrations leads to the poisoning of the service personnel.

In terms of its origin, natural gases are divided into two groups: dry and fat.

Dry Gases relate to mineral gases and are in areas related to the present or past activities of volcanoes. Dry gases consist almost exclusively from a single methane with an insignificant content of ballast components (nitrogen, carbon dioxide) and have the calorific value Q n \u003d 7000 ÷ 9000 kcal / nm3.

Fatty Gases accompany the oil fields and are usually accumulated in the upper layers. According to its origin, the fat gases are close to oil and contain many easily condensing hydrocarbons in their composition. The calorific value of liquid gases Q n \u003d 8000-15000 kcal / nm3

The advantages of gaseous fuels include the ease of transportation and combustion, the absence of moisture ash, significant simplicity of boiler equipment.

Along with natural gases, artificial combustible gases are used in the processing of solid fuels, or as a result of industrial installations as exhaust gases. Artificial gases consist of a combustible gas combustion of fuel, ballast gases and water vapors and are divided into rich and poor having an average calorific value of 4500 kcal / m3 and 1300 KC3, respectively. The composition of the gases: hydrogen, methane, other CMHN hydrocarbon compounds, hydrogen sulfide H 2 S, non-combustible gases, carbon dioxide, oxygen, nitrogen and a small amount of water vapor. Ballast - nitrogen and carbon dioxide.

Thus, the composition of dry gaseous fuel can be represented as the following mixture of elements:

CO + H 2 + ΣCMHN + H 2 S + CO 2 + O 2 + N 2 \u003d 100%.

The composition of wet gaseous fuel is expressed as follows:

Co + H 2 + ΣCMHN + H 2 S + CO 2 + O 2 + N 2 + H 2 O \u003d 100%.

Warm of combustion dry Gaseous fuel KJ / M3 (kcal / m3) per 1 m3 of gas under normal conditions are determined as follows:

QH \u003d 0.01,

Where Qi is the heat of combustion of the corresponding gas.

The heat of combustion of gaseous fuel is shown in Table 3.

Domain gas It is formed when smelting cast iron in blast furnaces. Its yield and himsows depend on the properties of the charge and fuel, the operation mode of the furnace, methods of intensifying the process and other factors. The yield of gas ranges from 1500-2500 m 3 per ton of cast iron. The proportion of non-combustible components (N 2 and CO 2) in the domain gas is about 70%, which causes its low heat engineering indicators (the lowest heat combustion of the gas is 3-5 mJ / m 3).

When burning a domain gas, the maximum temperature of combustion products (excluding thermal losses and heat consumption for dissociation CO 2 and H 2 O) is 400-1500 0 C. If you heat the gas and air before burning, then the temperature of combustion products can be significantly improved.

Ferroalloy gas It is formed during the smelting of ferroalloys in the rud-assessing furnaces. Gas, leaving closed furnaces, can be used as fuel WPER (secondary energy resources). In open furnaces, due to free air access, the gas burns on a rustic. The output and composition of ferroalloy gas depends on the brand of the paid

alloy, composition of the charge, operation of the furnace, its power, etc. Gas composition: 50-90% CO, 2-8% H 2, 0.3-1% CH 4, O 2<1%, 2-5% CO 2 , остальное N 2 . Максимальная температура продуктов сгорания равна 2080 ^0 C. Запылённость газа составляет 30-40 г/м^3 .

Converter gas It is formed when smelting steel in oxygen converters. Gas consists mainly of carbon oxide, the output and composition of it during the melting is significantly changed. After cleaning the composition of the gas approximately: 70-80% CO; 15-20% CO 2; 0.5-0.8% O 2; 3-12% N 2. Gas combustion contains 8.4-9.2 MJ / m 3. The maximum combustion temperature reaches 2000 0 S.

Coke gas It is formed during coal coal coal. In black metallurgy, it is used after the extraction of chemical products. The composition of the coke gas depends on the properties of the coal mixture and coking conditions. Volumented shares of components in Gaza are within the next limits,%: 52-62h 2; 0.3-0.6 o 2; 23.5-26.5 CH 4; 5.5-7.7 CO; 1.8-2.6 CO 2. The heat of the combustion is 17-17.6 MJ / M ^ 3, the maximum temperature of combustion products - 2070 0 C.

Gas fuel is divided into natural and artificial and is a mixture of combustible and non-combustible gases containing a certain amount of water vapor, and sometimes dust and resin. The amount of gas fuel is expressed in cubic meters under normal conditions (760 mm Hg. Art. And 0 ° C), and the composition - as a percentage by volume. Under the composition of the fuel understand the composition of its dry gaseous part.

Natural gas fuel

The most common gas fuel is natural gas with high heat combustion. The basis of natural gas is methane, the content of which is 76.7-98%. Other hydrocarbon gaseous compounds are part of natural gas from 0.1 to 4.5%.

Liquefied gas Product of oil refining - consists mainly of a mixture of propane and butane.

Natural gas (CNG, NG): methane CH4 more than 90%, ethane C2 H5 less than 4%, propane C3 H8 less than 1%

Liquefied gas (LPG): Propane C3 H8 more than 65%, Bhutan C4 H10 less than 35%

The composition of combustible gases includes: hydrogen H 2, methane CH 4, other hydrocarbon compounds with M H n, hydrogen sulfide H 2 S and non-combustible gases, carbon dioxide CO2, oxygen O 2, nitrogen N 2 and a slight amount of water vapor N 2 O. Indexes m. and pwith C and N, the compounds of various hydrocarbons are characterized, for example, for methane CH 4 t \u003d.1 I. n.\u003d 4, for ethane from 2N t \u003d 2.and n.\u003d B etc.

The composition of dry gaseous fuel (as a percentage of volume):

CO + H 2 + 2 C M N N + H 2 S + CO 2 + O 2 + N 2 \u003d 100%.

The non-combustible part of dry gas fuel is ballast - azot N and carbon dioxide CO 2.

The composition of wet gaseous fuel is expressed as follows:

Co + H 2 + σ with m n n + H 2 S + CO 2 + O 2 + N 2 + H 2 O \u003d 100%.

The heat of combustion, KJ / M (kcal / m 3), 1 m 3 of pure dry gas under normal conditions are determined as follows:

Q n c \u003d 0.01,

where qz, Q n 2, q with m n n q n 2 s. - heat of combustion of individual gases included in the mixture, KJ / m 3 (Kcal / m 3); Co, H 2,CM H N, H 2 S - Components constituting the gas mixture,% by volume.

The heat of combustion 1 m3 of dry natural gas under normal conditions for most domestic fields is 33.29 - 35.87 MJ / m3 (7946 - 8560 kcal / m3). The characteristic of the fuel gaseous is shown in Table 1.

Example.Determine the low heat of the combustion of natural gas (under normal conditions) of the following composition:

H 2 S \u003d 1%; CH 4 \u003d 76.7%; C 2 H 6 \u003d 4.5%; C 3 H 8 \u003d 1.7%; C 4 H 10 \u003d 0.8%; C 5 H 12 \u003d 0.6%.

Substituting in formula (26) the characteristics of the gases from Table 1, we obtain:

Q ns \u003d 0.01 \u003d 33981 kj / m 3 or

Q ns \u003d 0.01 (5585,1 + 8555 76,7 + 15 226 4.5 + 21 795 1.7 + 28 338 0.8 + 34 890 0.6) \u003d 8109 kcal / m 3.

Table 1. Characteristic of gaseous fuel

Gas	Designation	Heat combustionQ N S.
		KJ / M3.	Kcal / m3.
Hydrogen	N,	10820	2579
Oxigarbon	SO	12640	3018
Hydrogen sulfide	H 2 S.	23450	5585
Methane	CH 4.	35850	8555
Ethane	From 2N 6	63 850	15226
Propane	3H 8	91300	21795
Butane	From 4 H 10	118700	22338
Pentane	From 5 n 12	146200	34890
Ethylene	C 2N 4	59200	14107
Propylene	3H 6	85980	20541
Boutylene	From 4 H 8	113 400	27111
Benzene	From 6 H 6	140400	33528

DE boilers consume from 71 to 75 m3 of natural gas to obtain one ton of steam. The cost of gas in Russia for September 2008. It is 2.44 rubles per cubic meter. Consequently, the ton of the pair will cost 71 × 2.44 \u003d 173 rubles 24 kopecks. The real cost of a ton of steam on the factories is for the boilers de account to at least 189 rubles per ton of steam.

DCVR type boilers consume from 103 to 118 m3 of natural gas to obtain one ton of steam. The minimum calculation cost of a ton of steam for these boilers is 103 × 2.44 \u003d 251 rubles 32 kopecks. The real value of the steam on the plants is at least 290 rubles per ton.

How to calculate the maximum natural gas consumption on the de-25 steam boiler? This is the technical characteristics of the boiler. 1840 cubes per hour. But you can and calculate. 25 tons (25 thousand kg) must be multiplied by the difference in the enthalpium of steam and water (666.9-105) and all this is divided into kp. Bottop 92.8% and heat combustion of gas. 8300. And all

Artificial gas fuel

Artificial combustible gases are fuel of local significance, since they have a significantly less heat of combustion. The main combustible elements of them are carbon monoxide and hydrogen H2. These gases are used within the production where they are obtained as a fuel of technological and energy plants.

All natural and artificial combustible gases are explosive, are able to ignite on open fire or spark. The bottom and upper limit of the gas explosability are distinguished, i.e. The greatest and smallest percentage concentration in the air. The lower limit of the explosability of natural gases ranges from 3% to 6%, and the upper - from 12% to 16%. All combustible gases are able to cause human body poisoning. The main poisoning substances of flammable gases are: carbon monoxide, H2S hydrogen sulfide, NH3 ammonia.

Natural combustible gases and artificial colorless (invisible) do not smell, which makes them dangerous when penetrating into the inner room boiler room through looseness of gas reinforcement. In order to avoid poisoning, combustible gases should be treated by an alrode-substance with an unpleasant odor.

Obtaining carbon monoxide in industry solid fuel gasification

For industrial purposes, carbon monoxide is obtained by gasification of solid fuel, i.e. turning it into gaseous fuel. So you can get carbon monoxide from any solid fuel - fossil coal, peat, firewood, etc.

The process of gasification of solid fuel is shown on laboratory experiment (Fig. 1). Fill out a refractory tube with pieces of charcoal, heavily hesitate it and we will skip oxygen from a gasometer. Let out from the gas tube we will skip through the washing with limestone water and then impose. Lime water is trimmed, gas is burning a bluish flame. This indicates the presence of CO2 dioxide and carbon monoxide in the reaction products.

The formation of these substances can be explained by the fact that the latch is first oxidized in the carbon dioxide when contacting oxygen with hot coal. C + O 2 \u003d CO 2

Then, passing through the grilled coal, carbon dioxide is partially restored to them to carbon monoxide: CO 2 + C \u003d 2SO

Fig. 1. Getting carbon monoxide (laboratory experience).

In industrial conditions, solid fuel gasification is carried out in the furnaces called gas generators.

The resulting mixture of gases is called generator gas.

The gas generator device is shown in the figure. It is a steel cylinder with a height of about 5 m.and a diameter of about 3.5 m,futtered inside refractory brick. From above the gas generator is loaded with fuel; On the bottom through the grate with a fan, air or water vapor is served.

Air oxygen reacts with carbon fuel, forming carbon dioxide, which rises up through a layer of hot fuel, is restored by carbon to carbon monoxide.

If the generator is blowing only air, then gas is obtained, which in its composition contains carbon monoxide and air nitrogen (as well as a number of 2 and other impurities). Such generator gas is called air gas.

If the water vapor and hydrogen are formed as a result of the reaction, carbon and hydrogen are formed as a result of the reaction: C + H 2 O \u003d Co + H 2

This mixture of gases is called water gas. Water gas has a higher calorific value than air, as in its composition, along with carbon oxide, the second combustible gas is hydrogen. Water gas (gas synthesis), one of the fuel gasification products. Water gas consists mainly of CO (40%) and H2 (50%). Water gas is fuel (heat combustion of 10 500 kJ / m3, or 2730 kcal / mg) and at the same time raw materials for the synthesis of methyl alcohol. Water gas, however, cannot be obtained for a long time, since the formation reaction is its endothermic (with heat absorption), and therefore the fuel in the generator cools. To maintain coal in a split state, blowing the water vapor into the generator alternate with air intake, which is known, reacts with fuel with heat isolation.

Recently, steam-oxygen blur is widely used to gasify fuel. Simultaneous purging through a layer of fuel of water vapor and oxygen allows you to maintain the process continuously, significantly increase the production of the generator and receive gas with a high content of hydrogen and carbon monoxide.

Modern gas generators are powerful devices of continuous action.

In order for combustible and poisonous gases when applying fuel in the gas generator, the bootable drum is made double. While fuel enters into one branch of the drum, from another compartment, the fuel is poured into the generator; When rotating the drum, these processes are repeated, the generator remains isolated from the atmosphere all the time. Uniform fuel distribution in the generator is carried out using a cone that can be installed at different heights. When it is lowered, coal lies closer to the center of the generator, when the cone is raised, coal is discarded closer to the walls of the generator.

Removal of ash from the gas generator is mechanized. The grate grille having a cone shape slowly rotates the electric motor. At the same time, the ash shifts to the walls of the generator and the special adaptations are discharged into an rally box, from where it is periodically removed.

The first gas lights were lit in St. Petersburg at the Pharmaceutical Island in 1819. Gas, which was used, was obtained by gasification of coal. It was called the light gas.

The great Russian scientist D. I. Mendeleev (1834-1907) first expressed the idea that the gasification of coal can be made directly under the ground, without raising it out. The royal government did not appreciate this statement sentence.

The idea of \u200b\u200bunderground gasification was hotly supported by V. I. Lenin. He called her "one of the great victories of technology." Underground gasification was performed for the first time the Soviet state. Already before the Great Patriotic War in the Soviet Union, underground generators were worked in Donetsk and near Moscow coal basins.

The idea of \u200b\u200bone of the methods of underground gasification gives Figure 3. In the coal layer, two wells are packed, which are connected by the channel below. Coal is settled in such a channel at one of the wells and feed the pool there. The combustion products, moving along the channel, interact with grilled coal, resulting in a combustible gas as in a conventional generator. Gas goes to the surface through the second well.

Generator gas is widely used for heating industrial furnaces - metallurgical, cokes and as fuel in vehicles (Fig. 4).

Fig. 3. Scheme of underground gasification of stone coal.

A number of organic products are synthesized from hydrogen and carbon monoxide hydrogen, such as liquid fuel. Synthetic liquid fuel - fuel (mainly gasoline), obtained by synthesis of carbon monoxide and hydrogen at 150-170 gr Celsius and pressure 0.7 - 20 MN / M2 (200 kgf / cm2), in the presence of catalyst (nickel, iron, cobalt ). The first production of synthetic liquid fuel is organized in Germany during the 2nd World War due to the lack of oil. Wide propagation, synthetic liquid fuel did not receive due to its high cost. Water gas is used to produce hydrogen. For this, water gas in a water vapor mixture is heated in the presence of a catalyst and the result is hydrogen additionally to the already existing water gas: Co + H 2 O \u003d CO 2 + H 2

5. Top Balance of Burning

Consider methods for calculating the thermal balance of the process of burning gaseous, liquid and solid fuels. The calculation is reduced to solving the following tasks.

· Determination of the heat of burning (calorific value) of fuel.

· Definition of theoretical combustion temperature.

5.1. Heat burning

Chemical reactions are accompanied by the release or absorption of heat. When heat is isolated, the reaction is called exothermic, and when absorbed - endothermal. All combustion reactions are exothermic, and combustion products belong to exothermic compounds.

Allocated (or absorbed) during the flow of the chemical reaction of the heat is called the heat of the reaction. In exothermic reactions, it is positive, in endothermic - negative. The combustion reaction is always accompanied by the release of heat. Warm burning Q G. (J / mol) is called the amount of heat that stands out with the full combustion of one praying of the substance and turning the combustible substance into full combustion products. Mole is the main unit of the amount of substance in the SI system. One mole is such an amount of a substance in which there are as many particles (atoms, molecules, etc.), as containing atoms in 12 g of carbon isotope-12. The mass of a substance equal to 1 praying (molecular or molar mass) is numerically coincided with the relative molecular weight of this substance.

For example, the relative molecular weight of oxygen (O 2) is 32, carbon dioxide (CO 2) is 44, and the corresponding molecular weights will be equal to m \u003d 32 g / mol and m \u003d 44 g / mol. Thus, in one oxygen mole contains 32 grams of this substance, and in one CO 2 mole contains 44 grams of carbon dioxide.

No heat of burning is often used in technical calculations. Q G., and the calorific value of fuel Q.(J / kg or j / m 3). The calorific value of the substance is the amount of heat, which is allocated with full combustion of 1 kg or 1 m 3 of substances. For liquid and solids, the calculation is carried out by 1 kg, and for gaseous - by 1 m 3.

Knowledge of the heat of burning and calorific value of the fuel is necessary to calculate the temperature of burning or explosion, pressure during explosion, the rate of flame propagation and other characteristics. The calorific value of the fuel is determined by either experimental or estimated methods. In the experimental determination of the calorific value, the specified mass of solid or liquid fuel is burned in a calorimetric bomb, and in the case of gaseous fuels - in the gas calorimeter. Using these devices, the total heat is measured Q. 0, released when combustion of fuel suspension mass M.. The magnitude of the calorific value Q G. Located by formula

Communication between the warmth of burning and
The calorific value of fuel

To establish a connection between the heat of burning and the calorific value of the substance, it is necessary to record the equation of the chemical combustion reaction.

The product of complete combustion of carbon is carbon dioxide:

C + O 2 → CO 2.

The product of full burning of hydrogen is water:

2N 2 + O 2 → 2N 2 O.

The product of complete burning of sulfur is sulfur dioxide:

S + O 2 → SO 2.

At the same time stand out in the free form of nitrogen, halides and other non-combustible elements.

Fuel substance - gas

As an example, we will calculate the calorific value of methane CH 4, for which the heat of burning is equal to Q G.=882.6 .

· We define the molecular weight of methane in accordance with its chemical formula (CH 4):

M \u003d 1 ∙ 12 + 4 ∙ 1 \u003d 16 g / mol.

· Determine the calorific value of 1 kg of methane:

· Find a volume of 1 kg of methane, knowing its density ρ \u003d 0.717 kg / m 3 under normal conditions:

.

· Determine the calorific value of 1 m 3 of methane:

Similarly, the calorific value of any combustible gases is determined. For many common substances, the significance of the heat of burning and calorific value was measured with high accuracy and are given in the relevant reference literature. We present the table of values \u200b\u200bof the calorific value of some gaseous substances (Table 5.1). Value Q.this table is given in MJ / M 3 and in Kcal / m 3, since 1 kcal \u003d 4.1868 kJ is used as a unit of heat.

Table 5.1.

Calorous gaseous fuel

Substance			Acetylene
Q.

Fuel substance - liquid or solid body

As an example, we will calculate the calorific value of ethyl alcohol with 2 H 5, it, for which the heat of burning Q G. \u003d 1373.3 kJ / mol.

· We define the molecular weight of ethyl alcohol in accordance with its chemical formula (from 2 H 5):

M \u003d 2 ∙ 12 + 5 ∙ 1 + 1 ∙ 16 + 1 ∙ 1 \u003d 46 g / mol.

· Determine the calorific value of 1 kg of ethyl alcohol:

Similarly, the calorific value of any liquid and solid flammable is determined. In tab. 5.2 and 5.3 shows the values \u200b\u200bof calorific value Q.(MJ / kg and kcal / kg) for some liquid and solids.

Table 5.2.

Liquid fuel calorism

Substance		Methyl alcohol	Ethanol			Mazut, oil
Q.

Table 5.3.

Solid fuel calorific

Substance		Tree fresh	Dry tree	Brown coal	Peat dry	Anthracite, Cox
Q.

Formula Mendeleev

If the calorific value of the fuel is unknown, it can be calculated using the empirical formula proposed by D.I. Mendeleev. To do this, it is necessary to know the elemental composition of fuel (equivalent fuel formula), that is, the percentage of the following elements in it:

Oxygen (o);

Hydrogen (H);

Carbon (c);

Sulfur (s);

Ash (a);

Waters (W).

In the combustion products, fuels always contain pairs of water forming both due to the presence of moisture in fuel and during the combustion of hydrogen. Exhaust combustion products leave the industrial installation at temperatures above the temperature of the dew point. Therefore, heat that is allocated during the condensation of water vapor cannot be useful and should not be taken into account during thermal calculations.

For calculation, the lowest calorific value is usually applied. Q N. Fuel, which takes into account thermal losses with water vapor. For solid and liquid fuels Q N. (MJ / kg) is approximately determined by the Mendeleev formula:

Q N.=0.339+1.025+0.1085 – 0.1085 – 0.025, (5.1)

where in brackets indicated the percentage (wt.%) The content of the corresponding elements in the fuel composition.

This formula takes into account the heat of exothermic reactions of combustion of carbon, hydrogen and sulfur (with a "plus" sign). Oxygen included in the fuel partially replaces air oxygen, so the corresponding member in formula (5.1) is taken with a minus sign. When evaporation of moisture, the heat is consumed, therefore the corresponding term containing W is also taken with a "minus" sign.

Comparison of the calculated and experimental data on the calorific value of different fuels (wood, peat, coal, oil) showed that the calculation according to the Mendeleev formula (5.1) gives an error that does not exceed 10%.

Lower calorific value Q N. (MJ / M 3) Dry combustible gases with sufficient accuracy can be calculated as the sum of the products of the calorific value of individual components and their percentage of 1 m 3 of gaseous fuel.

Q N.\u003d 0.108 [H 2] + 0.126 [CO] + 0.358 [CH 4] + 0.5 [C 2 H 2] + 0.234 [H 2 S] ..., (5.2)

where in brackets indicated the percentage (volume.%) The content of the corresponding gases in the composition of the mixture.

On average, the calorific value of natural gas is approximately 53.6 MJ / m 3. In artificially obtained combustible gases, the content of methane CH 4 is slightly. The main combustible components are hydrogen H 2 and carbon oxide CO. In the coking gas, for example, the content of H 2 reaches (55 ÷ 60)%, and the lower calorific value of such gas reaches 17.6 MJ / m 3. In the generator gas, the content of ~ 30% and H 2 ~ 15%, while the lower calorific value of the generator gas Q N. \u003d (5.2 ÷ 6.5) MJ / M 3. In the domain gas, the content of CO and H 2 is less; Value Q N. \u003d (4.0 ÷ 4.2) MJ / m 3.

Consider examples of calculating the calorific value of substances according to the Mendeleev formula.

We define the calorific value of coal, the element composition is given in Table. 5.4.

Table 5.4.

The elemental composition of coal

· Substitute those shown in Table. 5.4 Data in the Mendeleev formula (5.1) (N and Azo Azot A in this formula is not included, since they are inert substances and do not participate in the combustion reaction):

Q N.\u003d 0.339 ∙ 37.2 + 1.025 ∙ 2.6 + 0.1085 ∙ 0.6-0.1085 ∙ 12-0.025 ∙ 40 \u003d 13.04 MJ / kg.

We define the amount of firewood needed for heating 50 liters of water from 10 ° C to 100 ° C if 5% of the heat released during burning is consumed, and the heat capacity of water is consumed from\u003d 1 kcal / (kg ∙ hail) or 4.1868 kJ / (kg ∙ hail). The elemental composition of firewood is given in Table. 5.5:

Table 5.5.

Elemental composition of wood

	· We will find the calorific value of firewood according to the Mendeleev formula (5.1): Q N.\u003d 0.339 ∙ 43 + 1.025 ∙ 7-0.1085 ∙ 41-0.025 ∙ 7 \u003d 17.12 MJ / kg. · We define the amount of heat consumed for water heating, during combustion of 1 kg of firewood (taking into account the fact that 5% of the heat is consumed on its heating (A \u003d 0.05), allocated during combustion): Q. 2 \u003d A. Q N.\u003d 0.05 · 17.12 \u003d 0.86 MJ / kg. · Determine the amount of firewood needed to heat 50 liters of water from 10 ° C to 100 ° C: kg. Thus, about 22 kg of firewood is required for water heating.